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This review summarizes recent progress in nickel-catalyzed arylative cyclizations of alkyne- and allene-tethered electrophiles using arylboron reagents, which are useful methods for the preparation of diverse carbo- and heterocyclic products. In many cases, nickel catalysis enables unique modes of reactivity not readily available to other metal catalysts. The scope of the reactions is discussed in detail, and general mechanistic concepts underpinning the processes are described. More information can be found in the review article by S.?M. Gillbard and H.?W. Lam et?al. (DOI: 10.1002/chem.202104230)

The use of arylboron reagents in metal-catalyzed domino addition–cyclization reactions is a well-established strategy for the preparation of diverse, highly functionalized carbo- and heterocyclic products. Although rhodium- and palladium-based catalysts have been commonly used for these reactions, more recent work has demonstrated nickel catalysis is also highly effective, in many cases offering unique reactivity and access to products that might otherwise not be readily available. This review gives an overview of nickel-catalyzed arylative cyclizations of alkyne- and allene-tethered electrophiles using arylboron reagents. The scope of the reactions is discussed in detail, and general mechanistic concepts underpinning the processes are described.

The synthesis of functionalized 1-tetralones by the rhodium(I)-catalyzed reaction of alkynyl malonates with arylboronic acids is described. These arylative cyclizations proceed via an alkenyl-to-aryl 1,4-Rh(I) migration as a key step. Preliminary results of an enantioselective variant of these reactions are also presented.

Nickel-catalyzed additions of arylboronic acids to alkynes, followed by enantioselective cyclizations of the alkenylnickel species onto tethered ketones or enones, are reported. These reactions are reliant upon the formal anti-carbonickelation of the alkyne, which is postulated to occur by the reversible E/Z isomerization of an alkenylnickel species.

A novel multicomponent coupling reaction involving the iridium-catalyzed 1,5-difunctionalization of 1,3-enynes with arylboronic acids and triazinanes is described. A key step in this 1,5-(aryl)aminomethylation reaction is the alkenyl-to-allyl 1,4-iridium(I) migration.

The enantioselective synthesis of highly functionalized chiral cyclopent-2-enones by the reaction of alkynyl malonate esters with arylboronic acids is described. These desymmetrizing arylative cyclizations are catalyzed by a chiral phosphinooxazoline–nickel complex, and cyclization is enabled by the reversible E/Z isomerization of alkenylnickel species. The general methodology is also applicable to the synthesis of 1,6-dihydropyridin-3(2H)- ones.

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim The enantioselective Cu-catalyzed 1,6-boration of (E,E)-α,β,γ,δ-unsaturated ketones is described, which gives homoallylic boronates with high enantiomeric purity and unexpectedly high Z-selectivity. By changing the solvent, the outcome can be altered to give E-allylic boronates.

Chiral cyclopentadienyl rhodium complexes promote highly enantioselective enol?directed C(sp2)?H functionalization and oxidative annulation with alkynes to give spiroindenes containing all?carbon quaternary stereocenters. High selectivity between two possible directing groups, as well as control of the direction of rotation in the isomerization of an O?bound rhodium enolate into the C?bound isomer, appear to be critical for high enantiomeric excesses.

Alkenyl-to-allyl 1,4-Rh(I) migration enables the generation of nucleophilic allylrhodium(I) species by remote C–H activation. This new mode of reactivity was employed in the diastereoselective reaction of arylboron reagents with substrates containing a 1,3-enyne tethered to a ketone, to give products containing three contiguous stereocenters. The products can be obtained in high enantioselectivities using a chiral sulfur–alkene ligand.

Chiral secondary allylboronates are obtained in high enantioselectivities by the copper-catalyzed 1,6-boration of electron-deficient dienes with B2(pin)2. The reactions proceed efficiently using catalyst loadings as low as 0.0049 mol%. The allylboronates may be oxidized to the allylic alcohols, and can be used in stereoselective aldehyde allylborations. This process was applied to a concise synthesis of atorvastatin.

Allylrhodium species derived from ?-trifluoroboryl ?,?-unsaturated esters undergo chain walking towards the ester moiety.The resulting allylrhodium species react with imines to give products containing two new stereocenters and a Z-alkene. By using a chiral diene ligand, products can be obtained with high enantioselectivities, where a pronounced matched/mismatched effect with the chirality of the allyltrifluoroborate is evident.